The present invention relates to venetian blind constructions in general and, in particular, to a new and useful venetian blind which utilizes a two-part carriage structure for supporting a lower one of a plurality of slats in a stack.
Such a venetian blind is disclosed in Swiss Pat. No. 565,935, for example. The draw member is usually an endless chain trained over a lower and an upper (driven) sprocket wheel and provided with an inserted intermediate piece which is guided in the casing, to which a supporting plate carrying an engaging member for the end pin of the lowermost slat is secured. This design has proven satisfactory in itself.
The conventional pivoting mechanism is readily responsive to the lowering or closing of the gathered blind, with the result that the slats which occupy a horizontal, open position in their gathered state are immediately pivoted into their almost vertical closing position. As soon as the blind is completely lowered or closed, all of the slats are closed. Since a reverse rotation of the windup shaft is necessary to open the slats, the blind is correspondingly lifted or opened due to the rigid connections between the lowermost slat and the draw member, which is undesirable.
Further, with a mechanical drive of the windup shaft and, consequently, of the draw member, it is difficult to set the motor to stop or be disengaged exactly upon reaching the lowermost end position. To ensure a complete lowering or lifting of the blind at any time, it is customary to insert a spring into the endless chain whose range of motion or action can absorb the inaccuracies of the motor setting. This of course can also be applied to designs wherein, as in the cited Swiss patent, means are associated with the pivoting mechanism for permitting only a limited pivoting of the slats during the lowering of the blind into a predetermined inclined position. That is, as soon as the blind with the inclined slats reaches its lower end position, the draw chain must continue its motion in the same direction, that is downwardly, to obtain a complete closure, which again can be effected only while using an intermediate spring. Such an intermediate spring, which is flexible in any direction, however, always makes the draw member relatively unstable, quite aside from the fact that, for example, an endless draw chain with an inserted intermediate spring is fairly expensive.
The present invention is directed to a venetian blind of the above specified kind which avoids the mentioned drawbacks and permits the use of a simple draw chain without an intermediate spring.
Accordingly, an object of the present invention is to provide a venetian blind, which comprises, a plurality of slats, with a pin extending from at least one side of each of said slats, a casing having a longitudinal slot for receiving each of said pins to permit longitudinal movement of the slats, collapsible support means interconnecting the plurality of slats for pivoting the slats as the slats are moved to extend and retract the venetian blind, a driven windup shaft rotatable on the casing, a draw member engaged with the windup shaft and movable in the casing by rotation of the shaft, an upper carriage part connected to one end of the draw member having a stop surface, an end stop on the casing against which the stop surface is abutable to stop movement of the draw member in one direction, a lower carriage part slidably connected to the upper carriage part and connected to a lowermost one of the slat pins, and spring means connected between the upper and lower carriage parts for biasing them apart, whereby, when the draw member is moved to extend the blind and is brought to a lowermost position of the lower carriage part, excess movement of the draw member is absorbed by the spring means.
The spring acting on the two carriage parts makes it possible to dispense with any additional intermediate spring in the draw member. Since the carriage reaches its lowermost position with its parts spread apart, a continued blind lowering movement of the draw member can only effect a further lowering and spring compressing motion of the upper carriage part, which motion may be utilized for pivoting the slats, for example, from their fully open or semi-open (inclined) position into their closing position, depending on which lowering position of the slats is provided.
A draw member design which has proved particularly advantageous is an open chain which is secured by one end to the upper carriage part, run over an upper sprocket wheel rotating with the windup shaft, and carries an end stop on its other end, limiting the lowering of the blind. Aside from the fact that the need for a lower sprocket wheel is eliminated, a substantial advantage of the inventive design is the shortness of this open chain requiring only a few chain links for securely engaging the upper sprocket wheel while the blind is lowered.
A further object of the present invention is to provide a venetian blind which is simple in design, rugged in construction and economical to manufacture.